Flash lamp circuit

Abstract

A circuit for repetitively firing a flash or strobe lamp with voltage derived from the AC line without large and costly storage capacitors utilizes a voltage doubler having small capacitors one microfarad in capacitance value or less. A trigger circuit provides a high potential pulse to the trigger electrode of the lamp at or near the peak of the voltage from the AC line to provide flashes at a desired rate, say one per second. The circuit may be used in a warning light device.

I claim: 
     
       1. A circuit for firing a flash lamp from AC power lines having a peak voltage less than the ionization voltage for initial arc conduction of said lamp when said lamp is fired which comprises means connected across the AC lines and across said lamp for storing energy for less than the period of a cycle of the AC voltage from said lines at a voltage higher than said ionization voltage for initial arc conduction and means included in said means connected across said lines for providing a direct path for current flow through said lamp from said lines continuously during said initial arc conduction and for sustaining arc conduction, said storing means consisting of the only energy storing means in the circuit for developing said ionization voltage for arc conduction of said lamp which are connected to said lamp, and means included in said storing means directly connecting said lamp across said lines to enable current flow from said lines through said lamp during ionization when said lamp fires, and means also connected to the AC lines and to said lamp for applying a trigger pulse to fire said lamp at or near the point during the said cycle when said peak voltage is reached and to enable current flow to said lamp from the AC lines. 
     
     
       2. The circuit according to claim 1 wherein said trigger pulse applying means include means for generating said trigger pulse repetitively to repetitively flash said lamp. 
     
     
       3. The circuit according to claim 1 wherein said energy storing means includes capacitors for storing said energy all of which are of value not exceeding one microfarads. 
     
     
       4. The circuit according to claim 3 wherein said storing means has a pair of diodes connected to said capacitors and in voltage multiplying relationship therewith. 
     
     
       5. The circuit according to claim 4 wherein said diodes are connected polarized in the same direction and in series with said lamp across said AC lines, one of said capacitors being connected between the junction of said diodes and the junction of said lamp and one side of said AC line, and the other of said capacitors being connected across both said diodes. 
     
     
       6. The circuit according to claim 5 wherein said capacitors are approximately equal in capacitance value. 
     
     
       7. The circuit according to claim 6 wherein the capacitance value of said capacitors is 0.1 microfarad or less. 
     
     
       8. The circuit according to claim 5 wherein said trigger pulse applying means comprises an SCR having an anode, a cathode and a gate, a pulse transformer having a primary and secondary windings, a pair of capacitors connected in series with each other across said AC line, a connection between one of said anode and cathode of said SCR and one side of said AC line, the other of said anode and cathode being connected to the junction of said pair of capacitors via the primary of said pulse transformer, means for determining the timing of said trigger pulse connecting said gate to at least one of a sides of said AC line, and means connecting said secondary to said flashlamp for applying said trigger pulse thereto. 
     
     
       9. The circuit according to claim 8 wherein said trigger pulse and timing determining means comprises a capacitor and diode connected in series across said AC lines and a resistor connected between said gate and the junction of said last named capacitor and diode. 
     
     
       10. The circuit according to claim 8 wherein said trigger pulse timing determining means comprises at least one resistor connected between said one of the sides of the said AC line and said gate and in parallel with said primary and one of said pair of capacitors via the gate and cathode of said SCR. 
     
     
       11. A flash lamp circuit operable from the AC power lines comprising a gas discharge flash lamp having main electrodes and a trigger electrode, a pair of diodes connected in series and polarized in the same direction between one side of the AC lines and one of said main electrodes, the other of said main electodes being connected to the other side of said AC lines, first and second capacitors of capacitance value of one microfarad or less and consisting the only means in said circuit for developing a voltage greater than the ionization voltage of said lamp for initial arc conduction when said lamp fires, said first capacitor being connected across said series connected diodes and directly connecting said one side of said AC lines to said one of said main electrodes thereby connecting said lamp directly across said AC lines to enable current flow to said lamp from said lines when said lamp fires, said second capacitor being connected between the junction of said diodes and the other of said main electrodes, and means connected to said trigger electrode and said AC lines for applying a trigger pulse at or near the peak voltage of the AC voltage to fire said lamp and enable current flow to said lamp from the AC lines. 
     
     
       12. The circuit according to claim 11 wherein said first and second capacitors are equal in capacitance value. 
     
     
       13. The circuit according to claim 12 wherein the capacitance value of said first and second capacitors is 0.01 microfarads. 
     
     
       14. The circuit according to claim 11 wherein said trigger pulse applying means comprises a pulse transformer having a primary and a secondary, a SCR having an anode, cathode and gate, third and fourth capacitors connected in series across the AC lines, a connection between one of said anode and cathode of said SCR and one side of said AC lines, the other of said anode and cathode being connected to the junction of said third and fourth capacitors via the primary of said pulse transformer, means for determining the timing of said trigger pulse connecting said gate to at least one of said sides of said AC lines and means connecting said secondary to said flashlamp trigger electrode. 
     
     
       15. The circuit according to claim 14 wherein said trigger pulse timing determining means comprises a fifth capacitor and third diode connected in series across said AC line, and a resistor connected between said gate and the junction of said fifth capacitor and third diode. 
     
     
       16. The circuit according to claim 14 wherein said trigger pulse timing determining means comprises at least one resistor connected between said one of the sides of said AC line and said gate and in parallel with said primary and said fourth capacitor via the gate and cathode of said SCR. 
     
     
       17. A circuit for firing a gas flash lamp from AC power lines, which lines provide the gas ionization sustaining current through said lamp, and without any storage capacitor for supplying the ionization sustaining current, said circuit comprising: first means, including at least one diode directly connecting said lines and said lamp, and connecting said lamp directly across said lines; for providing a direct path for current flow through said lamp from said lines continuously during said initial arc conduction and for sustaining arc conduction second means, including said diode, for developing a voltage of sufficient magnitude for initial arc conduction through said lamp at or near the peak of the AC voltage from said power lines and insufficient to maintain the ionization sustaining current through said lamp; and third means, connected to said lines and said lamp for applying a trigger pulse to fire said lamp at or near the peak of said AC voltage to enable the ionization sustaining current flow through said lamp from said lines. 
     
     
       18. The circuit according to claim 17 wherein said second means comprises at least one capacitor connected across said diode. 
     
     
       19. The circuit according to claim 18 wherein said one capacitor and any other capacitor in said circuit are of a value of one microfarad or less. 
     
     
       20. The circuit according to claim 18 wherein said second means includes means defining a voltage multiplying circuit for providing a DC voltage as said voltage of sufficient magnitude for initial arc conduction through said lamp.